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64r                           METALLURGY OF IRON AND STEEL.
a vertical distance of 15 feet, it is constantly reacting upon the* coke. Experiments show that a quantity of carbonic acid equal t« the amount liberated from the limestone is thus destroyed in the upper portions of the. furnace, with the production of an equivalent amount of carbonic oxide :(CO)» The energy of this carbonic oxidt? may be subsequently utilized under boilers or in the stoves, but it is totally lost as far as the economy of the furnace itself is concerned.                       ; .
, It is'not correct to say that all the carbonic acid from the stone is decomposed, for alongside of this amount is a certain quantity arising from the reaction between the ferrous oxide (FeO) and tlu» carbonic oxide (CO), and there is no warrant for supposing that a molecule 'of gas derived from the 'stone has any history different from a molecule derived from the reduction of theiore; but it may be said, for the sake of simplicity, that the reactions in the upper portion of the. furnace consist of the reduction of iron, oxides (:Fe2Os, Fe304, FeO) by carbonic oxide (CO) and the simultaneous oxidation of coke by the carbonic acid (C02) of the limestone, With the exception of this last reaction, and the formation of 11. small amount of carbon deposit, the coke charged at the top gora down through the furnace unchanged in quantity or condition until it reaches the immediate neighborhood of the tuyeres> f lift presence of so large a proportion of carbonic oxide rendering the oxidation of carbon out of the question.
• 'Below the place where the last of the FeO is'reduced, at a temperature of 800° C., at which point the limestone is decomposed, there are no reactions whatever occurring, and the whole history is one of heat absorption preparatory to the intense concentration of energy at the tuyeres. The-temperature, therefore, rises steadily and regularly as the tuyeres are approached. ' This rise in temperature is shown upon the diagram as being uniform throughout the entire height of the furnace, which is not strictly true, for the bosh region is cooled by water, and, being at a high temperature, the chilling effect at this point must be more rapid than will be found higher .'up, where there is little radiation and!no -heat-absorbing "reactions. There is another zone where the limestone is decomposed, and this portion would show a variation from a regular increase in. temperature, while above that point; considerable beat is absorbed by the union of carbonic acid from the stone'with